Inkjet printhead with thermal actuator coil

ABSTRACT

Provided is a printhead for an inkjet printer. The printhead has a plurality of micro-electromechanical ejection mechanisms arranged in a wafer substrate, with each mechanism having chamber walls and a roof formed on top of said substrate to define an ink chamber. One wall of the chamber defines a slot therein. The mechanism also includes an ink supply channel defined through the substrate to said chamber. The mechanism includes a bi-layer thermal actuator coil fast with the substrate and ending in a strut extending through the slot, said strut fast with a paddle device within the chamber.

CROSS-REFERENCES TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No. 12/139,493 filed Jun. 15, 2008, now issued Pat. No. 7,549,731, which is a continuation of U.S. application Ser. No. 11/056,146 filed Feb. 14, 2005, now issued Pat. No. 7,390,421, which is a continuation of U.S. application Ser. No. 09/113,076 filed Jul. 10, 1998, now issued Pat. No. 6,855,264, the entire contents of which are herein incorporated by reference.

CROSS REFERENCES TO RELATED APPLICATIONS

The following Australian provisional patent applications are hereby incorporated by cross-reference. For the purposes of location and identification, US patent applications identified by their U.S. patent application Ser. Nos. (USSN) are listed alongside the Australian applications from which the U.S. patent applications claim the right of priority.

US PATENT/ CROSS-REFERENCED PATENT APPLICATION AUSTRALIAN (CLAIMING RIGHT PROVISIONAL OF PRIORITY FROM PATENT AUSTRALIAN PROVISIONAL DOCKET APPLICATION NO. APPLICATION) NO. PO7991 6,750,901 ART01US PO8505 6,476,863 ART02US PO7988 6,788,336 ART03US PO9395 6,322,181 ART04US PO8017 6,597,817 ART06US PO8014 6,227,648 ART07US PO8025 6,727,948 ART08US PO8032 6,690,419 ART09US PO7999 6,727,951 ART10US PO8030 6,196,541 ART13US PO7997 6,195,150 ART15US PO7979 6,362,868 ART16US PO7978 6,831,681 ART18US PO7982 6,431,669 ART19US PO7989 6,362,869 ART20US PO8019 6,472,052 ART21US PO7980 6,356,715 ART22US PO8018 6,894,694 ART24US PO7938 6,636,216 ART25US PO8016 6,366,693 ART26US PO8024 6,329,990 ART27US PO7939 6,459,495 ART29US PO8501 6,137,500 ART30US PO8500 6,690,416 ART31US PO7987 7,050,143 ART32US PO8022 6,398,328 ART33US PO8497 7,110,024 ART34US PO8020 6,431,704 ART38US PO8504 6,879,341 ART42US PO8000 6,415,054 ART43US PO7934 6,665,454 ART45US PO7990 6,542,645 ART46US PO8499 6,486,886 ART47US PO8502 6,381,361 ART48US PO7981 6,317,192 ART50US PO7986 6,850,274 ART51US PO7983 09/113,054 ART52US PO8026 6,646,757 ART53US PO8028 6,624,848 ART56US PO9394 6,357,135 ART57US PO9397 6,271,931 ART59US PO9398 6,353,772 ART60US PO9399 6,106,147 ART61US PO9400 6,665,008 ART62US PO9401 6,304,291 ART63US PO9403 6,305,770 ART65US PO9405 6,289,262 ART66US PP0959 6,315,200 ART68US PP1397 6,217,165 ART69US PP2370 6,786,420 DOT01US PO8003 6,350,023 Fluid01US PO8005 6,318,849 Fluid02US PO8066 6,227,652 IJ01US PO8072 6,213,588 IJ02US PO8040 6,213,589 IJ03US PO8071 6,231,163 IJ04US PO8047 6,247,795 IJ05US PO8035 6,394,581 IJ06US PO8044 6,244,691 IJ07US PO8063 6,257,704 IJ08US PO8057 6,416,168 IJ09US PO8056 6,220,694 IJ10US PO8069 6,257,705 IJ11US PO8049 6,247,794 IJ12US PO8036 6,234,610 IJ13US PO8048 6,247,793 IJ14US PO8070 6,264,306 IJ15US PO8067 6,241,342 IJ16US PO8001 6,247,792 IJ17US PO8038 6,264,307 IJ18US PO8033 6,254,220 IJ19US PO8002 6,234,611 IJ20US PO8068 6,302,528 IJ21US PO8062 6,283,582 IJ22US PO8034 6,239,821 IJ23US PO8039 6,338,547 IJ24US PO8041 6,247,796 IJ25US PO8004 6,557,977 IJ26US PO8037 6,390,603 IJ27US PO8043 6,362,843 IJ28US PO8042 6,293,653 IJ29US PO8064 6,312,107 IJ30US PO9389 6,227,653 IJ31US PO9391 6,234,609 IJ32US PP0888 6,238,040 IJ33US PP0891 6,188,415 IJ34US PP0890 6,227,654 IJ35US PP0873 6,209,989 IJ36US PP0993 6,247,791 IJ37US PP0890 6,336,710 IJ38US PP1398 6,217,153 IJ39US PP2592 6,416,167 IJ40US PP2593 6,243,113 IJ41US PP3991 6,283,581 IJ42US PP3987 6,247,790 IJ43US PP3985 6,260,953 IJ44US PP3983 6,267,469 IJ45US PO7935 6,224,780 IJM01US PO7936 6,235,212 IJM02US PO7937 6,280,643 IJM03US PO8061 6,284,147 IJM04US PO8054 6,214,244 IJM05US PO8065 6,071,750 IJM06US PO8055 6,267,905 IJM07US PO8053 6,251,298 IJM08US PO8078 6,258,285 IJM09US PO7933 6,225,138 IJM10US PO7950 6,241,904 IJM11US PO7949 6,299,786 IJM12US PO8060 6,866,789 IJM13US PO8059 6,231,773 IJM14US PO8073 6,190,931 IJM15US PO8076 6,248,249 IJM16US PO8075 6,290,862 IJM17US PO8079 6,241,906 IJM18US PO8050 6,565,762 IJM19US PO8052 6,241,905 IJM20US PO7948 6,451,216 IJM21US PO7951 6,231,772 IJM22US PO8074 6,274,056 IJM23US PO7941 6,290,861 IJM24US PO8077 6,248,248 IJM25US PO8058 6,306,671 IJM26US PO8051 6,331,258 IJM27US PO8045 6,110,754 IJM28US PO7952 6,294,101 IJM29US PO8046 6,416,679 IJM30US PO9390 6,264,849 IJM31US PO9392 6,254,793 IJM32US PP0889 6,235,211 IJM35US PP0887 6,491,833 IJM36US PP0882 6,264,850 IJM37US PP0874 6,258,284 IJM38US PP1396 6,312,615 IJM39US PP3989 6,228,668 IJM40US PP2591 6,180,427 IJM41US PP3990 6,171,875 IJM42US PP3986 6,267,904 IJM43US PP3984 6,245,247 IJM44US PP3982 6,315,914 IJM45US PP0895 6,231,148 IR01US PP0869 6,293,658 IR04US PP0887 6,614,560 IR05US PP0885 6,238,033 IR06US PP0884 6,312,070 IR10US PP0886 6,238,111 IR12US PP0877 6,378,970 IR16US PP0878 6,196,739 IR17US PP0883 6,270,182 IR19US PP0880 6,152,619 IR20US PO8006 6,087,638 MEMS02US PO8007 6,340,222 MEMS03US PO8010 6,041,600 MEMS05US PO8011 6,299,300 MEMS06US PO7947 6,067,797 MEMS07US PO7944 6,286,935 MEMS09US PO7946 6,044,646 MEMS10US PP0894 6,382,769 MEMS13US

FIELD OF THE INVENTION

The present invention relates to the field of inkjet printing and, in particular, discloses a method of manufacture of an ink jet printer having a thermal actuator comprising an external coil spring.

BACKGROUND OF THE INVENTION

Many ink jet printing mechanisms are known. Unfortunately, in mass production techniques, the production of ink jet heads is quite difficult. For example, often, the orifice or nozzle plate is constructed separately from the ink supply and ink ejection mechanism and bonded to the mechanism at a later stage (Hewlett-Packard Journal, Vol. 36 no 5, pp33-37 (1985)). These separate material processing steps required in handling such precision devices often add a substantial expense in manufacturing.

Additionally, side shooting ink jet technologies (U.S. Pat. No. 4,899,181) are often used but again, this limits the amount of mass production throughput given any particular capital investment.

Additionally, more esoteric techniques are also often utilised. These can include electroforming of nickel stage (Hewlett-Packard Journal, Vol. 36 no 5, pp33-37 (1985)), electro-discharge machining, laser ablation (U.S. Pat. No. 5,208,604), micro-punching, etc.

The utilisation of the above techniques is likely to add substantial expense to the mass production of inkjet print heads and therefore add substantially to their final cost.

It would therefore be desirable if an efficient system for the mass production of ink jet print heads could be developed.

SUMMARY OF THE INVENTION

In accordance with an aspect of the present invention, there is provided a printhead for an inkjet printer, the printhead having a plurality of micro-electromechanical ejection mechanisms arranged in a wafer substrate, each mechanism comprising:

an ink chamber formed on said substrate, the ink chamber having an ink ejection nozzle formed in a roof thereof;

a paddle device arranged inside the ink chamber; and

a bi-layer thermal actuator coil fast with the substrate and outside the ink chamber, the thermal actuator coil being connected to the paddle device, wherein expansion of the thermal coil displaces the paddle device causing ejection of ink through the ink ejection nozzle.

Other aspects are also disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

Notwithstanding any other forms which may fall within the scope of the present invention, preferred forms of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

FIG. 1 illustrates a single ink ejection mechanism as constructed in accordance with the principles of the preferred embodiment;

FIG. 2 is a section through the line II-II of the actuator arm of FIG. 1;

FIGS. 3-5 illustrate the basic operation of the ink ejection mechanism of the preferred embodiment;

FIG. 6 is an exploded perspective view of an ink ejection mechanism.

FIG. 7 provides a legend of the materials indicated in FIGS. 8 to 22; and

FIG. 8 to FIG. 22 illustrate sectional views of the manufacturing steps in one form of construction of an ink jet printhead nozzle.

DESCRIPTION OF PREFERRED AND OTHER EMBODIMENTS

In the preferred embodiment, there is provided an inkjet printer having a series of ink ejection mechanisms wherein each ink ejection mechanism includes a paddle actuated by a coil actuator, the coil spring actuator having a unique cross section so as to provide for efficient actuation as a coiled thermal actuator.

Turning initially to FIG. 1, there is illustrated a single ink ejection mechanism 1 constructed in accordance with the principles of the preferred embodiment. The ink ejection mechanism 1 includes a chamber 2 having a rim 3. The chamber 2 is normally filled with ink which bulges out around a surface having a border along the edge of rim 3, the ink being retained within the chamber 2 by means of surface tension around the rim 3. Outside of the chamber 2 is located a thermal actuator device 5. The thermal actuator device 5 is interconnected via a strut 6 through a hole 7 to a paddle device within the chamber 2. The strut 6 and hole 7 are treated so as to be hydrophobic. Further, the hole 7 is provided in a thin elongated form so that surface tension characteristics also assist in stopping any ink from flowing out of the hole 7.

The thermal actuator device 5 comprises a first arm portion 9 which can be constructed from glass or other suitable non-conductive material. A second arm portion 10 can be constructed from material such as titanium diboride which has a large Young's modulus or bending strength and hence, when a current is passed through the titanium diboride layer 10, it expands with a predetermined coefficient of thermal expansion. The thin strip 10 has a high Young's modulus or bending strength and therefore the thin strip 10 is able to bend the much thicker strip 9 which has a substantially lower Young's modulus.

Turning to FIG. 2, there is illustrated a cross-section of the arm through the line II-II of FIG. 1 illustrating the structure of the actuator device 5. As described previously, the actuator device 5 includes two titanium diboride portions 10 a, 10 b forming a circuit around the coil in addition to the glass portion 9 which also provides for electrical isolation of the two arms, the arms being conductively joined at the strut end.

Turning now to FIGS. 3-5, there will now be explaining the operation of the ink ejection mechanism 1 for the ejection of ink. Initially, before the paddle 8 has started moving, the situation is as illustrated in FIG. 3 with the nozzle chamber 2 being filled with ink and having a slightly bulging meniscus 12. Upon actuation of the actuator mechanism, the paddle 8 begins to move towards the nozzle rim 3 resulting in a substantial increase in pressure in the area around the nozzle rim 3. This in turn results in the situation as illustrated in FIG. 4 wherein the meniscus begins to significantly bulge as a result of the increases in pressure. Subsequently, the actuator is deactivated resulting in a general urge for the paddle 8 to return to its rest position. This results in the ink being sucked back into the chamber 2 which in turn results in the meniscus necking and breaking off into a meniscus 12 and ink drop 14, the drop 14 proceeding to a paper or film medium (not shown) for marking. The meniscus 12 has generally a concave shape and surface tension characteristics result in chamber refilling by means of in flow 13 from an ink supply channel etched through the wafer. The refilling is as a consequence of surface tension forces on the meniscus 12. Eventually the meniscus returns to its quiescent state as illustrated in FIG. 3.

Turning now to FIG. 6, there is illustrated an exploded perspective view of a single ink ejection mechanism 1 illustrating the various material layers. The ink ejection mechanism 1 can be formed as part of a large array of mechanisms forming a print head with multiple print heads being simultaneously formed on a silicon wafer 17. The wafer 17 is initially processed so as to incorporate a standard CMOS circuitry layer 18 which provides for the electrical interconnect for the control of the conductive portions of the actuator. The CMOS layer 18 can be completed with a silicon nitride passivation layer so as to protect it from subsequent processing steps in addition to ink flows through channel 20. The subsequent layers eg. 9, 10 and 2 can be deposited utilising standard micro-electro mechanical systems (MEMS) construction techniques including the deposit of sacrificial aluminum layers in addition to the deposit of the layers 10 constructed from titanium diboride the layer 9 constructed from glass material and the nozzle chamber proper 2 again constructed from titanium diboride. Each of these layers can be built up in a sacrificial material such as aluminum which is subsequently etched away. Further, an ink supply channel eg. 21 can be etched through the wafer 17. The etching can be by means of an isotropic crystallographic silicon etch or an isotropic dry etch. A dry etch system capable of high aspect ratio silicon trench etching such as the Surface Technology Systems (STS) Advance Silicon Etch (ASE) system is recommended.

Subsequent to construction of the nozzle arrangement 1, it can be attached to an ink supply apparatus for supplying ink to the reverse surface of the wafer 17 so that ink can flow into chamber 2.

The external surface of nozzle chamber 2 including rim 3, in addition to the area surrounding slot 7, can then be hydrophobically treated so as to reduce the possibility of any ink exiting slot 7.

One form of detailed manufacturing process which can be used to fabricate monolithic ink jet print heads operating in accordance with the principles taught by the present embodiment can proceed utilizing the following steps:

-   1. Using a double sided polished wafer 17, Complete drive     transistors, data distribution, and timing circuits using a 0.5     micron, one poly, 2 metal CMOS process to form layer 18. This step     is shown in FIG. 8. For clarity, these diagrams may not be to scale,     and may not represent a cross section though any single plane of the     nozzle. FIG. 7 is a key to representations of various materials in     these manufacturing diagrams, and those of other cross referenced     ink jet configurations. -   2. Etch oxide layer 18 down to silicon or aluminum using Mask 1.     This mask defines the ink inlet, the heater contact vias, and the     edges of the print heads chip. This step is shown in FIG. 9. -   3. Deposit 1 micron of sacrificial material 30 (e.g. aluminum). -   4. Etch the sacrificial layer 30 using Mask 2, defining the nozzle     chamber wall and the actuator anchor point. This step is shown in     FIG. 10. -   5. Deposit 1 micron of glass 31. -   6. Etch the glass 31 using Mask 3, which defines the lower layer of     the actuator loop. -   7. Deposit 1 micron of heater material 32, for example titanium     nitride (TiN) or titanium diboride (TiB₂). Planarize using CMP.     Steps 5 to 7 form a ‘damascene’ process. This step is shown in FIG.     11. -   8. Deposit 0.1 micron of silicon nitride (not shown). -   9. Deposit 1 micron of glass 33. -   10. Etch the glass 33 using Mask 4, which defines the upper layer of     the actuator loop. -   11. Etch the silicon nitride using Mask 5, which defines the vias     connecting the upper layer of the actuator loop to the lower layer     of the actuator loop. -   12. Deposit 1 micron of the same heater material 34 as in step 7     heater material 32. Planarize using CMP. Steps 8 to 12 form a ‘dual     damascene’ process. This step is shown in FIG. 12. -   13. Etch the glass down to the sacrificial layer 30 using Mask 6,     which defines the actuator and the nozzle chamber wall, with the     exception of the nozzle chamber actuator slot. This step is shown in     FIG. 13. -   14. Wafer probe. All electrical connections are complete at this     point, bond pads are accessible, and the chips are not yet     separated. -   15. Deposit 3 microns of sacrificial material 35. -   16. Etch the sacrificial layer 35 down to glass using Mask 7, which     defines the nozzle chamber wall, with the exception of the nozzle     chamber actuator slot. This step is shown in FIG. 14. -   17. Deposit 1 micron of PECVD glass 36 and planarize down to the     sacrificial layer 35 using CMP. This step is shown in FIG. 15. -   18. Deposit 5 microns of sacrificial material 37. -   19. Etch the sacrificial material 37 down to glass using Mask 8.     This mask defines the nozzle chamber wall and the paddle. This step     is shown in FIG. 16. -   20. Deposit 3 microns of PECVD glass 38 and planarize down to the     sacrificial layer 37 using CMP. -   21. Deposit 1 micron of sacrificial material 39. -   22. Etch the sacrificial material 39 down to glass using Mask 9.     This mask defines the nozzle chamber wall. This step is shown in     FIG. 17. -   23. Deposit 3 microns of PECVD glass 40. -   24. Etch to a depth of (approx.) 1 micron using Mask 10. This mask     defines the nozzle rim 3. This step is shown in FIG. 18. -   25. Etch down to the sacrificial layer 39 using Mask 11. This mask     defines the roof of the nozzle chamber, and the nozzle itself This     step is shown in FIG. 19. -   26. Back-etch completely through the silicon wafer (with, for     example, an ASE Advanced Silicon Etcher from Surface Technology     Systems) using Mask 12. This mask defines the ink inlets 21 which     are etched through the wafer. The wafer is also diced by this etch.     This step is shown in FIG. 20. -   27. Etch the sacrificial material 30, 35, 37, 39. The nozzle     chambers are cleared, the actuators freed, and the chips are     separated by this etch. This step is shown in FIG. 21. -   28. Mount the print heads in their packaging, which may be a molded     plastic former incorporating ink channels which supply the     appropriate color ink to the ink inlets at the back of the wafer. -   29. Connect the print heads to their interconnect systems. For a low     profile connection with minimum disruption of airflow, TAB may be     used. Wire bonding may also be used if the printer is to be operated     with sufficient clearance to the paper. -   30. Hydrophobize the front surface of the print heads. -   31. Fill the completed print heads with ink 41 and test them. A     filled nozzle is shown in FIG. 22.

The presently disclosed ink jet printing technology is potentially suited to a wide range of printing system including: color and monochrome office printers, short run digital printers, high speed digital printers, offset press supplemental printers, low cost scanning printers high speed pagewidth printers, notebook computers with in-built pagewidth printers, portable color and monochrome printers, color and monochrome copiers, color and monochrome facsimile machines, combined printer, facsimile and copying machines, label printers, large format plotters, photograph copiers, printers for digital photographic “minilabs”, video printers, PHOTO CD (PHOTO CD is a registered trade mark of the Eastman Kodak Company) printers, portable printers for PDAs, wallpaper printers, indoor sign printers, billboard printers, fabric printers, camera printers and fault tolerant commercial printer arrays.

It would be appreciated by a person skilled in the art that numerous variations and/or modifications may be made to the present invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects to be illustrative and not restrictive.

Ink Jet Technologies

The embodiments of the invention use an ink jet printer type device. Of course many different devices could be used. However presently popular ink jet printing technologies are unlikely to be suitable.

The most significant problem with thermal ink jet is power consumption. This is approximately 100 times that required for high speed, and stems from the energy-inefficient means of drop ejection. This involves the rapid boiling of water to produce a vapor bubble which expels the ink. Water has a very high heat capacity, and must be superheated in thermal ink jet applications. This leads to an efficiency of around 0.02%, from electricity input to drop momentum (and increased surface area) out.

The most significant problem with piezoelectric ink jet is size and cost. Piezoelectric crystals have a very small deflection at reasonable drive voltages, and therefore require a large area for each nozzle. Also, each piezoelectric actuator must be connected to its drive circuit on a separate substrate. This is not a significant problem at the current limit of around 300 nozzles per print head, but is a major impediment to the fabrication of pagewidth print heads with 19,200 nozzles.

Ideally, the ink jet technologies used meet the stringent requirements of in-camera digital color printing and other high quality, high speed, low cost printing applications. To meet the requirements of digital photography, new ink jet technologies have been created. The target features include:

low power (less than 10 Watts)

high resolution capability (1,600 dpi or more)

photographic quality output

low manufacturing cost

small size (pagewidth times minimum cross section)

high speed (<2 seconds per page).

All of these features can be met or exceeded by the ink jet systems described below with differing levels of difficulty. Forty-five different ink jet technologies have been developed by the Assignee to give a wide range of choices for high volume manufacture. These technologies form part of separate applications assigned to the present Assignee as set out in the table above under the heading Cross References to Related Applications.

The ink jet designs shown here are suitable for a wide range of digital printing systems, from battery powered one-time use digital cameras, through to desktop and network printers, and through to commercial printing systems

For ease of manufacture using standard process equipment, the print head is designed to be a monolithic 0.5 micron CMOS chip with MEMS post processing. For color photographic applications, the print head is 100 mm long, with a width which depends upon the ink jet type. The smallest print head designed is IJ38, which is 0.35 mm wide, giving a chip area of 35 square mm. The print heads each contain 19,200 nozzles plus data and control circuitry.

Ink is supplied to the back of the print head by injection molded plastic ink channels. The molding requires 50 micron features, which can be created using a lithographically micromachined insert in a standard injection molding tool. Ink flows through holes etched through the wafer to the nozzle chambers fabricated on the front surface of the wafer. The print head is connected to the camera circuitry by tape automated bonding.

Tables of Drop-on-Demand Ink Jets

Eleven important characteristics of the fundamental operation of individual ink jet nozzles have been identified. These characteristics are largely orthogonal, and so can be elucidated as an eleven dimensional matrix. Most of the eleven axes of this matrix include entries developed by the present assignee.

The following tables form the axes of an eleven dimensional table of ink jet types.

Actuator mechanism (18 types)

Basic operation mode (7 types)

Auxiliary mechanism (8 types)

Actuator amplification or modification method (17 types)

Actuator motion (19 types)

Nozzle refill method (4 types)

Method of restricting back-flow through inlet (10 types)

Nozzle clearing method (9 types)

Nozzle plate construction (9 types)

Drop ejection direction (5 types)

Ink type (7 types)

The complete eleven dimensional table represented by these axes contains 36.9 billion possible configurations of inkjet nozzle. While not all of the possible combinations result in a viable ink jet technology, many million configurations are viable. It is clearly impractical to elucidate all of the possible configurations. Instead, certain ink jet types have been investigated in detail. These are designated IJ01 to IJ45 which matches the docket numbers in the in the table under the heading Cross References to Related Applications.

Other inkjet configurations can readily be derived from these forty-five examples by substituting alternative configurations along one or more of the 11 axes. Most of the IJ01 to IJ45 examples can be made into ink jet print heads with characteristics superior to any currently available ink jet technology.

Where there are prior art examples known to the inventor, one or more of these examples are listed in the examples column of the tables below. The IJ01 to IJ45 series are also listed in the examples column. In some cases, a printer may be listed more than once in a table, where it shares characteristics with more than one entry.

Suitable applications for the ink jet technologies include: Home printers, Office network printers, Short run digital printers, Commercial print systems, Fabric printers, Pocket printers, Internet WWW printers, Video printers, Medical imaging, Wide format printers, Notebook PC printers, Fax machines, Industrial printing systems, Photocopiers, Photographic minilabs etc.

The information associated with the aforementioned 11 dimensional matrix are set out in the following tables.

ACTUATOR MECHANISM (APPLIED ONLY TO SELECTED INK DROPS) Description Advantages Disadvantages Examples Thermal An electrothermal Large force High power Canon Bubblejet bubble heater heats the ink to generated Ink carrier limited to 1979 Endo et al GB above boiling point, Simple construction water patent 2,007,162 transferring significant No moving parts Low efficiency Xerox heater-in-pit heat to the aqueous Fast operation High temperatures 1990 Hawkins et al ink. A bubble Small chip area required U.S. Pat. No. 4,899,181 nucleates and quickly required for actuator High mechanical Hewlett-Packard TIJ forms, expelling the stress 1982 Vaught et al ink. Unusual materials U.S. Pat. No. 4,490,728 The efficiency of the required process is low, with Large drive typically less than transistors 0.05% of the electrical Cavitation causes energy being actuator failure transformed into Kogation reduces kinetic energy of the bubble formation drop. Large print heads are difficult to fabricate Piezo- A piezoelectric crystal Low power Very large area Kyser et al U.S. Pat. No. electric such as lead consumption required for actuator 3,946,398 lanthanum zirconate Many ink types can Difficult to integrate Zoltan U.S. Pat. No. (PZT) is electrically be used with electronics 3,683,212 activated, and either Fast operation High voltage drive 1973 Stemme U.S. Pat. No. expands, shears, or High efficiency transistors required 3,747,120 bends to apply Full pagewidth print Epson Stylus pressure to the ink, heads impractical Tektronix ejecting drops. due to actuator size IJ04 Requires electrical poling in high field strengths during manufacture Electro- An electric field is Low power Low maximum Seiko Epson, Usui strictive used to activate consumption strain (approx. et all JP 253401/96 electrostriction in Many ink types can 0.01%) IJ04 relaxor materials such be used Large area required as lead lanthanum Low thermal for actuator due to zirconate titanate expansion low strain (PLZT) or lead Electric field Response speed is magnesium niobate strength required marginal (~10 μs) (PMN). (approx. 3.5 V/μm) High voltage drive can be generated transistors required without difficulty Full pagewidth print Does not require heads impractical electrical poling due to actuator size Ferro- An electric field is Low power Difficult to integrate IJ04 electric used to induce a phase consumption with electronics transition between the Many ink types can Unusual materials antiferroelectric (AFE) be used such as PLZSnT are and ferroelectric (FE) Fast operation required phase. Perovskite (<1 μs) Actuators require a materials such as tin Relatively high large area modified lead longitudinal strain lanthanum zirconate High efficiency titanate (PLZSnT) Electric field exhibit large strains of strength of around 3 V/μm up to 1% associated can be readily with the AFE to FE provided phase transition. Electro- Conductive plates are Low power Difficult to operate IJ02, IJ04 static separated by a consumption electrostatic devices plates compressible or fluid Many ink types can in an aqueous dielectric (usually air). be used environment Upon application of a Fast operation The electrostatic voltage, the plates actuator will attract each other and normally need to be displace ink, causing separated from the drop ejection. The ink conductive plates may Very large area be in a comb or required to achieve honeycomb structure, high forces or stacked to increase High voltage drive the surface area and transistors may be therefore the force. required Full pagewidth print heads are not competitive due to actuator size Electro- A strong electric field Low current High voltage 1989 Saito et al, static pull is applied to the ink, consumption required U.S. Pat. No. 4,799,068 on ink whereupon Low temperature May be damaged by 1989 Miura et al, electrostatic attraction sparks due to air U.S. Pat. No. 4,810,954 accelerates the ink breakdown Tone-jet towards the print Required field medium. strength increases as the drop size decreases High voltage drive transistors required Electrostatic field attracts dust Permanent An electromagnet Low power Complex fabrication IJ07, IJ10 magnet directly attracts a consumption Permanent magnetic electro- permanent magnet, Many ink types can material such as magnetic displacing ink and be used Neodymium Iron causing drop ejection. Fast operation Boron (NdFeB) Rare earth magnets High efficiency required. with a field strength Easy extension from High local currents around 1 Tesla can be single nozzles to required used. Examples are: pagewidth print Copper metalization Samarium Cobalt heads should be used for (SaCo) and magnetic long materials in the electromigration neodymium iron boron lifetime and low family (NdFeB, resistivity NdDyFeBNb, Pigmented inks are NdDyFeB, etc) usually infeasible Operating temperature limited to the Curie temperature (around 540 K) Soft A solenoid induced a Low power Complex fabrication IJ01, IJ05, IJ08, magnetic magnetic field in a soft consumption Materials not IJ10, IJ12, IJ14, core magnetic core or yoke Many ink types can usually present in a IJ15, IJ17 electro- fabricated from a be used CMOS fab such as magnetic ferrous material such Fast operation NiFe, CoNiFe, or as electroplated iron High efficiency CoFe are required alloys such as CoNiFe Easy extension from High local currents [1], CoFe, or NiFe single nozzles to required alloys. Typically, the pagewidth print Copper metalization soft magnetic material heads should be used for is in two parts, which long are normally held electromigration apart by a spring. lifetime and low When the solenoid is resistivity actuated, the two parts Electroplating is attract, displacing the required ink. High saturation flux density is required (2.0-2.1 T is achievable with CoNiFe [1]) Lorenz The Lorenz force Low power Force acts as a IJ06, IJ11, IJ13, force acting on a current consumption twisting motion IJ16 carrying wire in a Many ink types can Typically, only a magnetic field is be used quarter of the utilized. Fast operation solenoid length This allows the High efficiency provides force in a magnetic field to be Easy extension from useful direction supplied externally to single nozzles to High local currents the print head, for pagewidth print required example with rare heads Copper metalization earth permanent should be used for magnets. long Only the current electromigration carrying wire need be lifetime and low fabricated on the print- resistivity head, simplifying Pigmented inks are materials usually infeasible requirements. Magneto- The actuator uses the Many ink types can Force acts as a Fischenbeck, U.S. Pat. No. striction giant magnetostrictive be used twisting motion 4,032,929 effect of materials Fast operation Unusual materials IJ25 such as Terfenol-D (an Easy extension from such as Terfenol-D alloy of terbium, single nozzles to are required dysprosium and iron pagewidth print High local currents developed at the Naval heads required Ordnance Laboratory, High force is Copper metalization hence Ter-Fe-NOL). available should be used for For best efficiency, the long actuator should be pre- electromigration stressed to approx. 8 MPa. lifetime and low resistivity Pre-stressing may be required Surface Ink under positive Low power Requires Silverbrook, EP tension pressure is held in a consumption supplementary force 0771 658 A2 and reduction nozzle by surface Simple construction to effect drop related patent tension. The surface No unusual separation applications tension of the ink is materials required in Requires special ink reduced below the fabrication surfactants bubble threshold, High efficiency Speed may be causing the ink to Easy extension from limited by surfactant egress from the single nozzles to properties nozzle. pagewidth print heads Viscosity The ink viscosity is Simple construction Requires Silverbrook, EP reduction locally reduced to No unusual supplementary force 0771 658 A2 and select which drops are materials required in to effect drop related patent to be ejected. A fabrication separation applications viscosity reduction can Easy extension from Requires special ink be achieved single nozzles to viscosity properties electrothermally with pagewidth print High speed is most inks, but special heads difficult to achieve inks can be engineered Requires oscillating for a 100:1 viscosity ink pressure reduction. A high temperature difference (typically 80 degrees) is required Acoustic An acoustic wave is Can operate without Complex drive 1993 Hadimioglu et generated and a nozzle plate circuitry al, EUP 550,192 focussed upon the Complex fabrication 1993 Elrod et al, drop ejection region. Low efficiency EUP 572,220 Poor control of drop position Poor control of drop volume Thermo- An actuator which Low power Efficient aqueous IJ03, IJ09, IJ17, elastic relies upon differential consumption operation requires a IJ18, IJ19, IJ20, bend thermal expansion Many ink types can thermal insulator on IJ21, IJ22, IJ23, actuator upon Joule heating is be used the hot side IJ24, IJ27, IJ28, used. Simple planar Corrosion IJ29, IJ30, IJ31, fabrication prevention can be IJ32, IJ33, IJ34, Small chip area difficult IJ35, IJ36, IJ37, required for each Pigmented inks may IJ38, IJ39, IJ40, actuator be infeasible, as IJ41 Fast operation pigment particles High efficiency may jam the bend CMOS compatible actuator voltages and currents Standard MEMS processes can be used Easy extension from single nozzles to pagewidth print heads High CTE A material with a very High force can be Requires special IJ09, IJ17, IJ18, thermo- high coefficient of generated material (e.g. PTFE) IJ20, IJ21, IJ22, elastic thermal expansion Three methods of Requires a PTFE IJ23, IJ24, IJ27, actuator (CTE) such as PTFE deposition are deposition process, IJ28, IJ29, IJ30, polytetrafluoroethylene under development: which is not yet IJ31, IJ42, IJ43, (PTFE) is used. As chemical vapor standard in ULSI IJ44 high CTE materials deposition (CVD), fabs are usually non- spin coating, and PTFE deposition conductive, a heater evaporation cannot be followed fabricated from a PTFE is a candidate with high conductive material is for low dielectric temperature (above incorporated. A 50 μm constant insulation 350° C.) processing long PTFE bend in ULSI Pigmented inks may actuator with Very low power be infeasible, as polysilicon heater and consumption pigment particles 15 mW power input Many ink types can may jam the bend can provide 180 μN be used actuator force and 10 μm Simple planar deflection. Actuator fabrication motions include: Small chip area Bend required for each Push actuator Buckle Fast operation Rotate High efficiency CMOS compatible voltages and currents Easy extension from single nozzles to pagewidth print heads Conductive A polymer with a high High force can be Requires special IJ24 polymer coefficient of thermal generated materials thermo- expansion (such as Very low power development (High elastic PTFE) is doped with consumption CTE conductive actuator conducting substances Many ink types can polymer) to increase its be used Requires a PTFE conductivity to about 3 Simple planar deposition process, orders of magnitude fabrication which is not yet below that of copper. Small chip area standard in ULSI The conducting required for each fabs polymer expands actuator PTFE deposition when resistively Fast operation cannot be followed heated. High efficiency with high Examples of CMOS compatible temperature (above conducting dopants voltages and 350° C.) processing include: currents Evaporation and Carbon nanotubes Easy extension from CVD deposition Metal fibers single nozzles to techniques cannot Conductive polymers pagewidth print be used such as doped heads Pigmented inks may polythiophene be infeasible, as Carbon granules pigment particles may jam the bend actuator Shape A shape memory alloy High force is Fatigue limits IJ26 memory such as TiNi (also available (stresses maximum number alloy known as Nitinol - of hundreds of MPa) of cycles Nickel Titanium alloy Large strain is Low strain (1%) is developed at the Naval available (more than required to extend Ordnance Laboratory) 3%) fatigue resistance is thermally switched High corrosion Cycle rate limited between its weak resistance by heat removal martensitic state and Simple construction Requires unusual its high stiffness Easy extension from materials (TiNi) austenic state. The single nozzles to The latent heat of shape of the actuator pagewidth print transformation must in its martensitic state heads be provided is deformed relative to Low voltage High current the austenic shape. operation operation The shape change Requires pre- causes ejection of a stressing to distort drop. the martensitic state Linear Linear magnetic Linear Magnetic Requires unusual IJ12 Magnetic actuators include the actuators can be semiconductor Actuator Linear Induction constructed with materials such as Actuator (LIA), Linear high thrust, long soft magnetic alloys Permanent Magnet travel, and high (e.g. CoNiFe) Synchronous Actuator efficiency using Some varieties also (LPMSA), Linear planar require permanent Reluctance semiconductor magnetic materials Synchronous Actuator fabrication such as Neodymium (LRSA), Linear techniques iron boron (NdFeB) Switched Reluctance Long actuator travel Requires complex Actuator (LSRA), and is available multi-phase drive the Linear Stepper Medium force is circuitry Actuator (LSA). available High current Low voltage operation operation

BASIC OPERATION MODE Description Advantages Disadvantages Examples Actuator This is the simplest Simple operation Drop repetition rate Thermal ink jet directly mode of operation: the No external fields is usually limited to Piezoelectric ink jet pushes ink actuator directly required around 10 kHz. IJ01, IJ02, IJ03, supplies sufficient Satellite drops can However, this is not IJ04, IJ05, IJ06, kinetic energy to expel be avoided if drop fundamental to the IJ07, IJ09, IJ11, the drop. The drop velocity is less than method, but is IJ12, IJ14, IJ16, must have a sufficient 4 m/s related to the refill IJ20, IJ22, IJ23, velocity to overcome Can be efficient, method normally IJ24, IJ25, IJ26, the surface tension. depending upon the used IJ27, IJ28, IJ29, actuator used All of the drop IJ30, IJ31, IJ32, kinetic energy must IJ33, IJ34, IJ35, be provided by the IJ36, IJ37, IJ38, actuator IJ39, IJ40, IJ41, Satellite drops IJ42, IJ43, IJ44 usually form if drop velocity is greater than 4.5 m/s Proximity The drops to be Very simple print Requires close Silverbrook, EP printed are selected by head fabrication can proximity between 0771 658 A2 and some manner (e.g. be used the print head and related patent thermally induced The drop selection the print media or applications surface tension means does not need transfer roller reduction of to provide the May require two pressurized ink). energy required to print heads printing Selected drops are separate the drop alternate rows of the separated from the ink from the nozzle image in the nozzle by Monolithic color contact with the print print heads are medium or a transfer difficult roller. Electro- The drops to be Very simple print Requires very high Silverbrook, EP static pull printed are selected by head fabrication can electrostatic field 0771 658 A2 and on ink some manner (e.g. be used Electrostatic field related patent thermally induced The drop selection for small nozzle applications surface tension means does not need sizes is above air Tone-Jet reduction of to provide the breakdown pressurized ink). energy required to Electrostatic field Selected drops are separate the drop may attract dust separated from the ink from the nozzle in the nozzle by a strong electric field. Magnetic The drops to be Very simple print Requires magnetic Silverbrook, EP pull on ink printed are selected by head fabrication can ink 0771 658 A2 and some manner (e.g. be used Ink colors other than related patent thermally induced The drop selection black are difficult applications surface tension means does not need Requires very high reduction of to provide the magnetic fields pressurized ink). energy required to Selected drops are separate the drop separated from the ink from the nozzle in the nozzle by a strong magnetic field acting on the magnetic ink. Shutter The actuator moves a High speed (>50 kHz) Moving parts are IJ13, IJ17, IJ21 shutter to block ink operation can required flow to the nozzle. The be achieved due to Requires ink ink pressure is pulsed reduced refill time pressure modulator at a multiple of the Drop timing can be Friction and wear drop ejection very accurate must be considered frequency. The actuator energy Stiction is possible can be very low Shuttered The actuator moves a Actuators with Moving parts are IJ08, IJ15, IJ18, grill shutter to block ink small travel can be required IJ19 flow through a grill to used Requires ink the nozzle. The shutter Actuators with pressure modulator movement need only small force can be Friction and wear be equal to the width used must be considered of the grill holes. High speed (>50 kHz) Stiction is possible operation can be achieved Pulsed A pulsed magnetic Extremely low Requires an external IJ10 magnetic field attracts an ‘ink energy operation is pulsed magnetic pull on ink pusher’ at the drop possible field pusher ejection frequency. An No heat dissipation Requires special actuator controls a problems materials for both catch, which prevents the actuator and the the ink pusher from ink pusher moving when a drop is Complex not to be ejected. construction

AUXILIARY MECHANISM (APPLIED TO ALL NOZZLES) Description Advantages Disadvantages Examples None The actuator directly Simplicity of Drop ejection Most ink jets, fires the ink drop, and construction energy must be including there is no external Simplicity of supplied by piezoelectric and field or other operation individual nozzle thermal bubble. mechanism required. Small physical size actuator IJ01, IJ02, IJ03, IJ04, IJ05, IJ07, IJ09, IJ11, IJ12, IJ14, IJ20, IJ22, IJ23, IJ24, IJ25, IJ26, IJ27, IJ28, IJ29, IJ30, IJ31, IJ32, IJ33, IJ34, IJ35, IJ36, IJ37, IJ38, IJ39, IJ40, IJ41, IJ42, IJ43, IJ44 Oscillating The ink pressure Oscillating ink Requires external Silverbrook, EP ink oscillates, providing pressure can provide ink pressure 0771 658 A2 and pressure much of the drop a refill pulse, oscillator related patent (including ejection energy. The allowing higher Ink pressure phase applications acoustic actuator selects which operating speed and amplitude must IJ08, IJ13, IJ15, stimulation) drops are to be fired The actuators may be carefully IJ17, IJ18, IJ19, by selectively operate with much controlled IJ21 blocking or enabling lower energy Acoustic reflections nozzles. The ink Acoustic lenses can in the ink chamber pressure oscillation be used to focus the must be designed may be achieved by sound on the for vibrating the print nozzles head, or preferably by an actuator in the ink supply. Media The print head is Low power Precision assembly Silverbrook, EP proximity placed in close High accuracy required 0771 658 A2 and proximity to the print Simple print head Paper fibers may related patent medium. Selected construction cause problems applications drops protrude from Cannot print on the print head further rough substrates than unselected drops, and contact the print medium. The drop soaks into the medium fast enough to cause drop separation. Transfer Drops are printed to a High accuracy Bulky Silverbrook, EP roller transfer roller instead Wide range of print Expensive 0771 658 A2 and of straight to the print substrates can be Complex related patent medium. A transfer used construction applications roller can also be used Ink can be dried on Tektronix hot melt for proximity drop the transfer roller piezoelectric ink jet separation. Any of the IJ series Electro- An electric field is Low power Field strength Silverbrook, EP static used to accelerate Simple print head required for 0771 658 A2 and selected drops towards construction separation of small related patent the print medium. drops is near or applications above air Tone-Jet breakdown Direct A magnetic field is Low power Requires magnetic Silverbrook, EP magnetic used to accelerate Simple print head ink 0771 658 A2 and field selected drops of construction Requires strong related patent magnetic ink towards magnetic field applications the print medium. Cross The print head is Does not require Requires external IJ06, IJ16 magnetic placed in a constant magnetic materials magnet field magnetic field. The to be integrated in Current densities Lorenz force in a the print head may be high, current carrying wire manufacturing resulting in is used to move the process electromigration actuator. problems Pulsed A pulsed magnetic Very low power Complex print head IJ10 magnetic field is used to operation is possible construction field cyclically attract a Small print head Magnetic materials paddle, which pushes size required in print on the ink. A small head actuator moves a catch, which selectively prevents the paddle from moving.

ACTUATOR AMPLIFICATION OR MODIFICATION METHOD Description Advantages Disadvantages Examples None No actuator Operational Many actuator Thermal Bubble Ink mechanical simplicity mechanisms have jet amplification is used. insufficient travel, IJ01, IJ02, IJ06, The actuator directly or insufficient force, IJ07, IJ16, IJ25, drives the drop to efficiently drive IJ26 ejection process. the drop ejection process Differential An actuator material Provides greater High stresses are Piezoelectric expansion expands more on one travel in a reduced involved IJ03, IJ09, IJ17, bend side than on the other. print head area Care must be taken IJ18, IJ19, IJ20, actuator The expansion may be that the materials do IJ21, IJ22, IJ23, thermal, piezoelectric, not delaminate IJ24, IJ27, IJ29, magnetostrictive, or Residual bend IJ30, IJ31, IJ32, other mechanism. The resulting from high IJ33, IJ34, IJ35, bend actuator converts temperature or high IJ36, IJ37, IJ38, a high force low travel stress during IJ39, IJ42, IJ43, actuator mechanism to formation IJ44 high travel, lower force mechanism. Transient A trilayer bend Very good High stresses are IJ40, IJ41 bend actuator where the two temperature stability involved actuator outside layers are High speed, as a Care must be taken identical. This cancels new drop can be that the materials do bend due to ambient fired before heat not delaminate temperature and dissipates residual stress. The Cancels residual actuator only responds stress of formation to transient heating of one side or the other. Reverse The actuator loads a Better coupling to Fabrication IJ05, IJ11 spring spring. When the the ink complexity actuator is turned off, High stress in the the spring releases. spring This can reverse the force/distance curve of the actuator to make it compatible with the force/time requirements of the drop ejection. Actuator A series of thin Increased travel Increased Some piezoelectric stack actuators are stacked. Reduced drive fabrication ink jets This can be voltage complexity IJ04 appropriate where Increased possibility actuators require high of short circuits due electric field strength, to pinholes such as electrostatic and piezoelectric actuators. Multiple Multiple smaller Increases the force Actuator forces may IJ12, IJ13, IJ18, actuators actuators are used available from an not add linearly, IJ20, IJ22, IJ28, simultaneously to actuator reducing efficiency IJ42, IJ43 move the ink. Each Multiple actuators actuator need provide can be positioned to only a portion of the control ink flow force required. accurately Linear A linear spring is used Matches low travel Requires print head IJ15 Spring to transform a motion actuator with higher area for the spring with small travel and travel requirements high force into a Non-contact method longer travel, lower of motion force motion. transformation Coiled A bend actuator is Increases travel Generally restricted IJ17, IJ21, IJ34, actuator coiled to provide Reduces chip area to planar IJ35 greater travel in a Planar implementations reduced chip area. implementations are due to extreme relatively easy to fabrication difficulty fabricate. in other orientations. Flexure A bend actuator has a Simple means of Care must be taken IJ10, IJ19, IJ33 bend small region near the increasing travel of not to exceed the actuator fixture point, which a bend actuator elastic limit in the flexes much more flexure area readily than the Stress distribution is remainder of the very uneven actuator. The actuator Difficult to flexing is effectively accurately model converted from an with finite element even coiling to an analysis angular bend, resulting in greater travel of the actuator tip. Catch The actuator controls a Very low actuator Complex IJ10 small catch. The catch energy construction either enables or Very small actuator Requires external disables movement of size force an ink pusher that is Unsuitable for controlled in a bulk pigmented inks manner. Gears Gears can be used to Low force, low Moving parts are IJ13 increase travel at the travel actuators can required expense of duration. be used Several actuator Circular gears, rack Can be fabricated cycles are required and pinion, ratchets, using standard More complex drive and other gearing surface MEMS electronics methods can be used. processes Complex construction Friction, friction, and wear are possible Buckle A buckle plate can be Very fast movement Must stay within S. Hirata et al, “An plate used to change a slow achievable elastic limits of the Ink-jet Head Using actuator into a fast materials for long Diaphragm motion. It can also device life Microactuator”, convert a high force, High stresses Proc. IEEE MEMS, low travel actuator involved February 1996, pp 418-423. into a high travel, Generally high IJ18, IJ27 medium force motion. power requirement Tapered A tapered magnetic Linearizes the Complex IJ14 magnetic pole can increase magnetic construction pole travel at the expense force/distance curve of force. Lever A lever and fulcrum is Matches low travel High stress around IJ32, IJ36, IJ37 used to transform a actuator with higher the fulcrum motion with small travel requirements travel and high force Fulcrum area has no into a motion with linear movement, longer travel and and can be used for lower force. The lever a fluid seal can also reverse the direction of travel. Rotary The actuator is High mechanical Complex IJ28 impeller connected to a rotary advantage construction impeller. A small The ratio of force to Unsuitable for angular deflection of travel of the actuator pigmented inks the actuator results in can be matched to a rotation of the the nozzle impeller vanes, which requirements by push the ink against varying the number stationary vanes and of impeller vanes out of the nozzle. Acoustic A refractive or No moving parts Large area required 1993 Hadimioglu et lens diffractive (e.g. zone Only relevant for al, EUP 550,192 plate) acoustic lens is acoustic ink jets 1993 Elrod et al, used to concentrate EUP 572,220 sound waves. Sharp A sharp point is used Simple construction Difficult to fabricate Tone-jet conductive to concentrate an using standard VLSI point electrostatic field. processes for a surface ejecting ink- jet Only relevant for electrostatic ink jets

ACTUATOR MOTION Description Advantages Disadvantages Examples Volume The volume of the Simple construction High energy is Hewlett-Packard expansion actuator changes, in the case of typically required to Thermal Ink jet pushing the ink in all thermal ink jet achieve volume Canon Bubblejet directions. expansion. This leads to thermal stress, cavitation, and kogation in thermal ink jet implementations Linear, The actuator moves in Efficient coupling to High fabrication IJ01, IJ02, IJ04, normal to a direction normal to ink drops ejected complexity may be IJ07, IJ11, IJ14 chip the print head surface. normal to the required to achieve surface The nozzle is typically surface perpendicular in the line of motion movement. Parallel to The actuator moves Suitable for planar Fabrication IJ12, IJ13, IJ15, chip parallel to the print fabrication complexity IJ33,, IJ34, IJ35, surface head surface. Drop Friction IJ36 ejection may still be Stiction normal to the surface. Membrane An actuator with a The effective area of Fabrication 1982 Howkins U.S. Pat. No. push high force but small the actuator complexity 4,459,601 area is used to push a becomes the Actuator size stiff membrane that is membrane area Difficulty of in contact with the ink. integration in a VLSI process Rotary The actuator causes Rotary levers may Device complexity IJ05, IJ08, IJ13, the rotation of some be used to increase May have friction at IJ28 element, such a grill or travel a pivot point impeller Small chip area requirements Bend The actuator bends A very small change Requires the 1970 Kyser et al when energized. This in dimensions can actuator to be made U.S. Pat. No. 3,946,398 may be due to be converted to a from at least two 1973 Stemme U.S. Pat. No. differential thermal large motion. distinct layers, or to 3,747,120 expansion, have a thermal IJ03, IJ09, IJ10, piezoelectric difference across the IJ19, IJ23, IJ24, expansion, actuator IJ25, IJ29, IJ30, magnetostriction, or IJ31, IJ33, IJ34, other form of relative IJ35 dimensional change. Swivel The actuator swivels Allows operation Inefficient coupling IJ06 around a central pivot. where the net linear to the ink motion This motion is suitable force on the paddle where there are is zero opposite forces Small chip area applied to opposite requirements sides of the paddle, e.g. Lorenz force. Straighten The actuator is Can be used with Requires careful IJ26, IJ32 normally bent, and shape memory balance of stresses straightens when alloys where the to ensure that the energized. austenitic phase is quiescent bend is planar accurate Double The actuator bends in One actuator can be Difficult to make IJ36, IJ37, IJ38 bend one direction when used to power two the drops ejected by one element is nozzles. both bend directions energized, and bends Reduced chip size. identical. the other way when Not sensitive to A small efficiency another element is ambient temperature loss compared to energized. equivalent single bend actuators. Shear Energizing the Can increase the Not readily 1985 Fishbeck U.S. Pat. No. actuator causes a shear effective travel of applicable to other 4,584,590 motion in the actuator piezoelectric actuator material. actuators mechanisms Radial The actuator squeezes Relatively easy to High force required 1970 Zoltan U.S. Pat. No. constriction an ink reservoir, fabricate single Inefficient 3,683,212 forcing ink from a nozzles from glass Difficult to integrate constricted nozzle. tubing as with VLSI macroscopic processes structures Coil/ A coiled actuator Easy to fabricate as Difficult to fabricate IJ17, IJ21, IJ34, uncoil uncoils or coils more a planar VLSI for non-planar IJ35 tightly. The motion of process devices the free end of the Small area required, Poor out-of-plane actuator ejects the ink. therefore low cost stiffness Bow The actuator bows (or Can increase the Maximum travel is IJ16, IJ18, IJ27 buckles) in the middle speed of travel constrained when energized. Mechanically rigid High force required Push-Pull Two actuators control The structure is Not readily suitable IJ18 a shutter. One actuator pinned at both ends, for ink jets which pulls the shutter, and so has a high out-of- directly push the ink the other pushes it. plane rigidity Curl A set of actuators curl Good fluid flow to Design complexity IJ20, IJ42 inwards inwards to reduce the the region behind volume of ink that the actuator they enclose. increases efficiency Curl A set of actuators curl Relatively simple Relatively large IJ43 outwards outwards, pressurizing construction chip area ink in a chamber surrounding the actuators, and expelling ink from a nozzle in the chamber. Iris Multiple vanes enclose High efficiency High fabrication IJ22 a volume of ink. These Small chip area complexity simultaneously rotate, Not suitable for reducing the volume pigmented inks between the vanes. Acoustic The actuator vibrates The actuator can be Large area required 1993 Hadimioglu et vibration at a high frequency. physically distant for efficient al, EUP 550,192 from the ink operation at useful 1993 Elrod et al, frequencies EUP 572,220 Acoustic coupling and crosstalk Complex drive circuitry Poor control of drop volume and position None In various ink jet No moving parts Various other Silverbrook, EP designs the actuator tradeoffs are 0771 658 A2 and does not move. required to related patent eliminate moving applications parts Tone-jet

NOZZLE REFILL METHOD Description Advantages Disadvantages Examples Surface This is the normal way Fabrication Low speed Thermal ink jet tension that ink jets are simplicity Surface tension Piezoelectric ink jet refilled. After the Operational force relatively IJ01-IJ07, IJ10-IJ14, actuator is energized, simplicity small compared to IJ16, IJ20, IJ22-IJ45 it typically returns actuator force rapidly to its normal Long refill time position. This rapid usually dominates return sucks in air the total repetition through the nozzle rate opening. The ink surface tension at the nozzle then exerts a small force restoring the meniscus to a minimum area. This force refills the nozzle. Shuttered Ink to the nozzle High speed Requires common IJ08, IJ13, IJ15, oscillating chamber is provided at Low actuator ink pressure IJ17, IJ18, IJ19, ink a pressure that energy, as the oscillator IJ21 pressure oscillates at twice the actuator need only May not be suitable drop ejection open or close the for pigmented inks frequency. When a shutter, instead of drop is to be ejected, ejecting the ink drop the shutter is opened for 3 half cycles: drop ejection, actuator return, and refill. The shutter is then closed to prevent the nozzle chamber emptying during the next negative pressure cycle. Refill After the main High speed, as the Requires two IJ09 actuator actuator has ejected a nozzle is actively independent drop a second (refill) refilled actuators per nozzle actuator is energized. The refill actuator pushes ink into the nozzle chamber. The refill actuator returns slowly, to prevent its return from emptying the chamber again. Positive The ink is held a slight High refill rate, Surface spill must Silverbrook, EP ink positive pressure. therefore a high be prevented 0771 658 A2 and pressure After the ink drop is drop repetition rate Highly hydrophobic related patent ejected, the nozzle is possible print head surfaces applications chamber fills quickly are required Alternative for:, as surface tension and IJ01-IJ07, IJ10-IJ14, ink pressure both IJ16, IJ20, IJ22-IJ45 operate to refill the nozzle.

METHOD OF RESTRICTING BACK-FLOW THROUGH INLET Description Advantages Disadvantages Examples Long inlet The ink inlet channel Design simplicity Restricts refill rate Thermal ink jet channel to the nozzle chamber Operational May result in a Piezoelectric ink jet is made long and simplicity relatively large chip IJ42, IJ43 relatively narrow, Reduces crosstalk area relying on viscous Only partially drag to reduce inlet effective back-flow. Positive The ink is under a Drop selection and Requires a method Silverbrook, EP ink positive pressure, so separation forces (such as a nozzle 0771 658 A2 and pressure that in the quiescent can be reduced rim or effective related patent state some of the ink Fast refill time hydrophobizing, or applications drop already protrudes both) to prevent Possible operation from the nozzle. flooding of the of the following: This reduces the ejection surface of IJ01-IJ07, IJ09-IJ12, pressure in the nozzle the print head. IJ14, IJ16, chamber which is IJ20, IJ22,, IJ23-IJ34, required to eject a IJ36-IJ41, certain volume of ink. IJ44 The reduction in chamber pressure results in a reduction in ink pushed out through the inlet. Baffle One or more baffles The refill rate is not Design complexity HP Thermal Ink Jet are placed in the inlet as restricted as the May increase Tektronix ink flow. When the long inlet method. fabrication piezoelectric ink jet actuator is energized, Reduces crosstalk complexity (e.g. the rapid ink Tektronix hot melt movement creates Piezoelectric print eddies which restrict heads). the flow through the inlet. The slower refill process is unrestricted, and does not result in eddies. Flexible In this method recently Significantly Not applicable to Canon flap disclosed by Canon, reduces back-flow most ink jet restricts the expanding actuator for edge-shooter configurations inlet (bubble) pushes on a thermal ink jet Increased flexible flap that devices fabrication restricts the inlet. complexity Inelastic deformation of polymer flap results in creep over extended use Inlet filter A filter is located Additional Restricts refill rate IJ04, IJ12, IJ24, between the ink inlet advantage of ink May result in IJ27, IJ29, IJ30 and the nozzle filtration complex chamber. The filter Ink filter may be construction has a multitude of fabricated with no small holes or slots, additional process restricting ink flow. steps The filter also removes particles which may block the nozzle. Small inlet The ink inlet channel Design simplicity Restricts refill rate IJ02, IJ37, IJ44 compared to the nozzle chamber May result in a to nozzle has a substantially relatively large chip smaller cross section area than that of the nozzle, Only partially resulting in easier ink effective egress out of the nozzle than out of the inlet. Inlet A secondary actuator Increases speed of Requires separate IJ09 shutter controls the position of the ink-jet print refill actuator and a shutter, closing off head operation drive circuit the ink inlet when the main actuator is energized. The inlet is The method avoids the Back-flow problem Requires careful IJ01, IJ03, IJ05, located problem of inlet back- is eliminated design to minimize IJ06, IJ07, IJ10, behind the flow by arranging the the negative IJ11, IJ14, IJ16, ink- ink-pushing surface of pressure behind the IJ22, IJ23, IJ25, pushing the actuator between paddle IJ28, IJ31, IJ32, surface the inlet and the IJ33, IJ34, IJ35, nozzle. IJ36, IJ39, IJ40, IJ41 Part of the The actuator and a Significant Small increase in IJ07, IJ20, IJ26, actuator wall of the ink reductions in back- fabrication IJ38 moves to chamber are arranged flow can be complexity shut off so that the motion of achieved the inlet the actuator closes off Compact designs the inlet. possible Nozzle In some configurations Ink back-flow None related to ink Silverbrook, EP actuator of ink jet, there is no problem is back-flow on 0771 658 A2 and does not expansion or eliminated actuation related patent result in movement of an applications ink back- actuator which may Valve-jet flow cause ink back-flow Tone-jet through the inlet.

NOZZLE CLEARING METHOD Description Advantages Disadvantages Examples Normal All of the nozzles are No added May not be Most ink jet systems nozzle fired periodically, complexity on the sufficient to IJ01, IJ02, IJ03, firing before the ink has a print head displace dried ink IJ04, IJ05, IJ06, chance to dry. When IJ07, IJ09, IJ10, not in use the nozzles IJ11, IJ12, IJ14, are sealed (capped) IJ16, IJ20, IJ22, against air. IJ23, IJ24, IJ25, The nozzle firing is IJ26, IJ27, IJ28, usually performed IJ29, IJ30, IJ31, during a special IJ32, IJ33, IJ34, clearing cycle, after IJ36, IJ37, IJ38, first moving the print IJ39, IJ40,, IJ41, head to a cleaning IJ42, IJ43, IJ44,, station. IJ45 Extra In systems which heat Can be highly Requires higher Silverbrook, EP power to the ink, but do not boil effective if the drive voltage for 0771 658 A2 and ink heater it under normal heater is adjacent to clearing related patent situations, nozzle the nozzle May require larger applications clearing can be drive transistors achieved by over- powering the heater and boiling ink at the nozzle. Rapid The actuator is fired in Does not require Effectiveness May be used with: succession rapid succession. In extra drive circuits depends IJ01, IJ02, IJ03, of some configurations, on the print head substantially upon IJ04, IJ05, IJ06, actuator this may cause heat Can be readily the configuration of IJ07, IJ09, IJ10, pulses build-up at the nozzle controlled and the ink jet nozzle IJ11, IJ14, IJ16, which boils the ink, initiated by digital IJ20, IJ22, IJ23, clearing the nozzle. In logic IJ24, IJ25, IJ27, other situations, it may IJ28, IJ29, IJ30, cause sufficient IJ31, IJ32, IJ33, vibrations to dislodge IJ34, IJ36, IJ37, clogged nozzles. IJ38, IJ39, IJ40, IJ41, IJ42, IJ43, IJ44, IJ45 Extra Where an actuator is A simple solution Not suitable where May be used with: power to not normally driven to where applicable there is a hard limit IJ03, IJ09, IJ16, ink the limit of its motion, to actuator IJ20, IJ23, IJ24, pushing nozzle clearing may be movement IJ25, IJ27, IJ29, actuator assisted by providing IJ30, IJ31, IJ32, an enhanced drive IJ39, IJ40, IJ41, signal to the actuator. IJ42, IJ43, IJ44, IJ45 Acoustic An ultrasonic wave is A high nozzle High IJ08, IJ13, IJ15, resonance applied to the ink clearing capability implementation cost IJ17, IJ18, IJ19, chamber. This wave is can be achieved if system does not IJ21 of an appropriate May be already include an amplitude and implemented at very acoustic actuator frequency to cause low cost in systems sufficient force at the which already nozzle to clear include acoustic blockages. This is actuators easiest to achieve if the ultrasonic wave is at a resonant frequency of the ink cavity. Nozzle A microfabricated Can clear severely Accurate Silverbrook, EP clearing plate is pushed against clogged nozzles mechanical 0771 658 A2 and plate the nozzles. The plate alignment is related patent has a post for every required applications nozzle. A post moves Moving parts are through each nozzle, required displacing dried ink. There is risk of damage to the nozzles Accurate fabrication is required Ink The pressure of the ink May be effective Requires pressure May be used with pressure is temporarily where other pump or other all IJ series ink jets pulse increased so that ink methods cannot be pressure actuator streams from all of the used Expensive nozzles. This may be Wasteful of ink used in conjunction with actuator energizing. Print head A flexible ‘blade’ is Effective for planar Difficult to use if Many ink jet wiper wiped across the print print head surfaces print head surface is systems head surface. The Low cost non-planar or very blade is usually fragile fabricated from a Requires flexible polymer, e.g. mechanical parts rubber or synthetic Blade can wear out elastomer. in high volume print systems Separate A separate heater is Can be effective Fabrication Can be used with ink boiling provided at the nozzle where other nozzle complexity many IJ series ink heater although the normal clearing methods jets drop e-ection cannot be used mechanism does not Can be implemented require it. The heaters at no additional cost do not require in some ink jet individual drive configurations circuits, as many nozzles can be cleared simultaneously, and no imaging is required.

NOZZLE PLATE CONSTRUCTION Description Advantages Disadvantages Examples Electro- A nozzle plate is Fabrication High temperatures Hewlett Packard formed separately fabricated simplicity and pressures are Thermal Ink jet nickel from electroformed required to bond nickel, and bonded to nozzle plate the print head chip. Minimum thickness constraints Differential thermal expansion Laser Individual nozzle No masks required Each hole must be Canon Bubblejet ablated or holes are ablated by an Can be quite fast individually formed 1988 Sercel et al., drilled intense UV laser in a Some control over Special equipment SPIE, Vol. 998 polymer nozzle plate, which is nozzle profile is required Excimer Beam typically a polymer possible Slow where there Applications, pp. such as polyimide or Equipment required are many thousands 76-83 polysulphone is relatively low cost of nozzles per print 1993 Watanabe et head al., U.S. Pat. No. 5,208,604 May produce thin burrs at exit holes Silicon A separate nozzle High accuracy is Two part K. Bean, IEEE micro- plate is attainable construction Transactions on machined micromachined from High cost Electron Devices, single crystal silicon, Requires precision Vol. ED-25, No. 10, and bonded to the alignment 1978, pp 1185-1195 print head wafer. Nozzles may be Xerox 1990 clogged by adhesive Hawkins et al., U.S. Pat. No. 4,899,181 Glass Fine glass capillaries No expensive Very small nozzle 1970 Zoltan U.S. Pat. No. capillaries are drawn from glass equipment required sizes are difficult to 3,683,212 tubing. This method Simple to make form has been used for single nozzles Not suited for mass making individual production nozzles, but is difficult to use for bulk manufacturing of print heads with thousands of nozzles. Monolithic, The nozzle plate is High accuracy (<1 μm) Requires sacrificial Silverbrook, EP surface deposited as a layer Monolithic layer under the 0771 658 A2 and micro- using standard VLSI Low cost nozzle plate to form related patent machined deposition techniques. Existing processes the nozzle chamber applications using VLSI Nozzles are etched in can be used Surface may be IJ01, IJ02, IJ04, litho- the nozzle plate using fragile to the touch IJ11, IJ12, IJ17, graphic VLSI lithography and IJ18, IJ20, IJ22, processes etching. IJ24, IJ27, IJ28, IJ29, IJ30, IJ31, IJ32, IJ33, IJ34, IJ36, IJ37, IJ38, IJ39, IJ40, IJ41, IJ42, IJ43, IJ44 Monolithic, The nozzle plate is a High accuracy (<1 μm) Requires long etch IJ03, IJ05, IJ06, etched buried etch stop in the Monolithic times IJ07, IJ08, IJ09, through wafer. Nozzle Low cost Requires a support IJ10, IJ13, IJ14, substrate chambers are etched in No differential wafer IJ15, IJ16, IJ19, the front of the wafer, expansion IJ21, IJ23, IJ25, and the wafer is IJ26 thinned from the back side. Nozzles are then etched in the etch stop layer. No nozzle Various methods have No nozzles to Difficult to control Ricoh 1995 Sekiya plate been tried to eliminate become clogged drop position et al U.S. Pat. No. 5,412,413 the nozzles entirely, to accurately 1993 Hadimioglu et prevent nozzle Crosstalk problems al EUP 550,192 clogging. These 1993 Elrod et al include thermal bubble EUP 572,220 mechanisms and acoustic lens mechanisms Trough Each drop ejector has Reduced Drop firing IJ35 a trough through manufacturing direction is sensitive which a paddle moves. complexity to wicking. There is no nozzle Monolithic plate. Nozzle slit The elimination of No nozzles to Difficult to control 1989 Saito et al instead of nozzle holes and become clogged drop position U.S. Pat. No. 4,799,068 individual replacement by a slit accurately nozzles encompassing many Crosstalk problems actuator positions reduces nozzle clogging, but increases crosstalk due to ink surface waves

DROP EJECTION DIRECTION Description Advantages Disadvantages Examples Edge Ink flow is along the Simple construction Nozzles limited to Canon Bubblejet (‘edge surface of the chip, No silicon etching edge 1979 Endo et al GB shooter’) and ink drops are required High resolution is patent 2,007,162 ejected from the chip Good heat sinking difficult Xerox heater-in-pit edge. via substrate Fast color printing 1990 Hawkins et al Mechanically strong requires one print U.S. Pat. No. 4,899,181 Ease of chip head per color Tone-jet handing Surface Ink flow is along the No bulk silicon Maximum ink flow Hewlett-Packard TIJ (‘roof surface of the chip, etching required is severely restricted 1982 Vaught et al shooter’) and ink drops are Silicon can make an U.S. Pat. No. 4,490,728 ejected from the chip effective heat sink IJ02, IJ11, IJ12, surface, normal to the Mechanical strength IJ20, IJ22 plane of the chip. Through Ink flow is through the High ink flow Requires bulk Silverbrook, EP chip, chip, and ink drops are Suitable for silicon etching 0771 658 A2 and forward ejected from the front pagewidth print related patent (‘up surface of the chip. heads applications shooter’) High nozzle packing IJ04, IJ17, IJ18, density therefore IJ24, IJ27-IJ45 low manufacturing cost Through Ink flow is through the High ink flow Requires wafer IJ01, IJ03, IJ05, chip, chip, and ink drops are Suitable for thinning IJ06, IJ07, IJ08, reverse ejected from the rear pagewidth print Requires special IJ09, IJ10, IJ13, (‘down surface of the chip. heads handling during IJ14, IJ15, IJ16, shooter’) High nozzle packing manufacture IJ19, IJ21, IJ23, density therefore IJ25, IJ26 low manufacturing cost Through Ink flow is through the Suitable for Pagewidth print Epson Stylus actuator actuator, which is not piezoelectric print heads require Tektronix hot melt fabricated as part of heads several thousand piezoelectric ink jets the same substrate as connections to drive the drive transistors. circuits Cannot be manufactured in standard CMOS fabs Complex assembly required

INK TYPE Description Advantages Disadvantages Examples Aqueous, Water based ink which Environmentally Slow drying Most existing ink dye typically contains: friendly Corrosive jets water, dye, surfactant, No odor Bleeds on paper All IJ series ink jets humectant, and May strikethrough Silverbrook, EP biocide. Cockles paper 0771 658 A2 and Modern ink dyes have related patent high water-fastness, applications light fastness Aqueous, Water based ink which Environmentally Slow drying IJ02, IJ04, IJ21, pigment typically contains: friendly Corrosive IJ26, IJ27, IJ30 water, pigment, No odor Pigment may clog Silverbrook, EP surfactant, humectant, Reduced bleed nozzles 0771 658 A2 and and biocide. Reduced wicking Pigment may clog related patent Pigments have an Reduced actuator applications advantage in reduced strikethrough mechanisms Piezoelectric ink- bleed, wicking and Cockles paper jets strikethrough. Thermal ink jets (with significant restrictions) Methyl MEK is a highly Very fast drying Odorous All IJ series ink jets Ethyl volatile solvent used Prints on various Flammable Ketone for industrial printing substrates such as (MEK) on difficult surfaces metals and plastics such as aluminum cans. Alcohol Alcohol based inks Fast drying Slight odor All IJ series ink jets (ethanol, can be used where the Operates at sub- Flammable 2-butanol, printer must operate at freezing and temperatures below temperatures others) the freezing point of Reduced paper water. An example of cockle this is in-camera Low cost consumer photographic printing. Phase The ink is solid at No drying time-ink High viscosity Tektronix hot melt change room temperature, and instantly freezes on Printed ink typically piezoelectric ink jets (hot melt) is melted in the print the print medium has a ‘waxy’ feel 1989 Nowak U.S. Pat. No. head before jetting. Almost any print Printed pages may 4,820,346 Hot melt inks are medium can be used ‘block’ All IJ series ink jets usually wax based, No paper cockle Ink temperature with a melting point occurs may be above the around 80° C. After No wicking occurs curie point of jetting the ink freezes No bleed occurs permanent magnets almost instantly upon No strikethrough Ink heaters consume contacting the print occurs power medium or a transfer Long warm-up time roller. Oil Oil based inks are High solubility High viscosity: this All IJ series ink jets extensively used in medium for some is a significant offset printing. They dyes limitation for use in have advantages in Does not cockle ink jets, which improved paper usually require a characteristics on Does not wick low viscosity. Some paper (especially no through paper short chain and wicking or cockle). multi-branched oils Oil soluble dies and have a sufficiently pigments are required. low viscosity. Slow drying Micro- A microemulsion is a Stops ink bleed Viscosity higher All IJ series ink jets emulsion stable, self forming High dye solubility than water emulsion of oil, water, Water, oil, and Cost is slightly and surfactant. The amphiphilic soluble higher than water characteristic drop size dies can be used based ink is less than 100 nm, Can stabilize High surfactant and is determined by pigment concentration the preferred curvature suspensions required (around of the surfactant. 5%) 

1. A printhead for an inkjet printer, the printhead having a plurality of micro-electromechanical ejection mechanisms arranged in a wafer substrate, each mechanism comprising: an ink chamber formed on said substrate, the ink chamber having an ink ejection nozzle formed in a roof thereof; a paddle device arranged inside the ink chamber; and a bi-layer thermal actuator coil fast with the substrate and outside the ink chamber, the thermal actuator coil being connected to the paddle device, wherein expansion of the thermal coil displaces the paddle device causing ejection of ink through the ink ejection nozzle.
 2. The printhead as claimed in claim 1, wherein the bi-layer thermal actuator coil includes a first layer manufactured from a non-conductive material and a second layer manufactured from a conductive material, wherein applying current to the second later causes the thermal actuator coil to expand.
 3. The printhead as claimed in claim 2, wherein the first layer is manufactured from glass and the second layer is manufactured from titanium diboride.
 4. The printhead as claimed in claim 3, wherein the substrate includes a CMOS layer arranged in electrical communication with the second layer.
 5. The printhead as claimed in claim 1, wherein the thermal actuator coil is connected to the paddle device by a strut extending through an aperture in a side wall of the ink chamber.
 6. The printhead as claimed in claim 5, wherein the strut and the aperture are treated to be hydrophobic.
 7. The printhead as claimed in claim 5, wherein the aperture has a thin elongate form.
 8. The printhead as claimed in claim 1, wherein a rim is formed around a perimeter of the ink nozzle, the rim being configured to exploit surface tension characteristics of ink in the chamber to prevent ink from flowing out of the chamber. 